Real time monitoring over the state of cargo is especially important in long-distance transport of various goods by vessels, trucks or by railway transport. To preserve the goods during transportation, it is desirable to maintain various parameters, such as, temperature inside a container within a specified range. In addition to temperature, it may be desirable to maintain humidity, gas composition and other parameters inside container within a specified range.
One example of such monitoring is a telemetry system measuring one or more parameters within a transport container and transmitting a signal indicating the value or values of the one or more measured parameters, or of the status of the respective transport container. Such signal transmission occurs via at least one communication network. This system includes a receiving station connected to the communication network, sensor-based means for monitoring intended for the reception of a signal corresponding to the measured parameters. The system also includes mobile monitoring subsystem installed on the container or inside it and generating a signal corresponding to the values of measured parameters or to the container status. If the measured parameters stay within predetermined limits, the subsystem generates a status signal indicating that the system is operating properly. When the measured parameters fall outside these limits, the subsystem generates a signal indicating the values of measured parameters. Also, such subsystem includes a local communication means for transmitting a signal to a reception station and means of monitoring usage of at least one communication network.
Another example is a system capable of adjusting the temperature in the container cargo compartment under the control of the refrigerator controller. This system performs remote control of the reefer equipment operation using the networks of short-range radio communication and cellular communication networks. However, this system has limited functional capabilities, because it is a specialized system with two communication channels without reprogramming ability. Moreover, short range communication can be performed only with specialized control panel. This system can not provide remote monitoring and control if cellular network is unavailable.
In the systems intended for remote monitoring and control of refrigerator transport containers equipment, gathering of information on equipment operation, transmission of collected information to the central station, and reception of instructions for the correction of perishable goods transportation conditions is usually carried out by a special computerized unit—namely, reefer equipment monitoring and control device, which is located inside or outside the container. Different designs of such devices are known.
For example, a monitoring terminal device including a sensors unit, a unit for wireless signal transmission connected to the sensors unit, and a power source (in particular, a solar battery could be used as such) with a control unit for said power source is known. The device is intended only for remote control of different devices; however, it is incapable of controlling the modes of their operation.
Another example is a wireless monitoring unit which includes sensors, a microprocessor, a memory unit intended for storage of data and programs for microprocessor, a power source, and a radio transceiver intended for the transmission of commands received from information sensors and for the reception of commands and data from a user. This device is unable to control the reefer equipment operation.
Another example of a device includes a monitoring unit connected to the reefer equipment of a container and receiving current information on the conditions of perishable goods within container from the reefer equipment. The device also includes a memory unit intended for the storage of current information, a transceiver for short-range and long-range radio communication with the control unit and a unit for identification of container location based on GPS-receiver. This device is unable to control the reefer equipment operation directly based on signals received from the remote central station.
Yet another example of a device includes a local communication transmitter, a cellular communication transmitter, a local communication receiver, and a cellular communication receiver. However, this device has limited functional capabilities. For example, short range communication can be performed only with specialized control panel. This device can not provide remote monitoring and control if cellular network is unavailable.